The reaction employing CuCN is well known in the art and is sometimes called the Rosenmund-von Braun Reaction. The reaction can schematically be represented by: EQU ArX+CuCN.fwdarw.ArCN+CuX
wherein X represents a halogen atom and the reaction is carried out at a temperature of about 150.degree.-250.degree. C. The reaction is carried out in a variety of solvents, the most commonly employed solvents being polar aprotic solvents such as dimethylformamide, dimethylacetamide and N-methylpyrrolidone. Commonly, an excess of CuCN is employed.
An example of such a process is the preparation of p-hydroxybenzonitrile (HBN) from p-halogenated phenol, which can conveniently be carried out in dimethylacetamide (DMA) as the solvent.
When the reaction is complete the solvent is normally distilled off and the nitrile product is obtained as a complex bound to the cuprous halide which is formed in the reaction. In order to isolate the nitrile product, the complex must be decomposed. Several methods are known in the art to effect this decomposition. In one such method [U.S. Pat. No. 3,259,646] concentrated hydrochloric acid and ferric chloride are added and the product is isolated by extraction into an organic solvent. According to another method [L. Freidman and H. Schechter, J. Org. Chem., Vol. 26, pp. 2522-24 (1961)], ethylene diamine is added and the product is again isolated by solvent extraction. According to a further known method, the cuprous halide is dissolved in an aqeous solution containing 4 molar equivalents of NaCN and the product is extracted with an organic solvent.
The aforementioned and other known isolation methods present several serious drawbacks. The copper halide formed in the reaction is transformed into difficulty recoverable forms, which cannot be recycled as such. Furthermore, in the first mentioned method the formation of highly toxic hydrogen cyanide and cyanogen takes place. In the last two methods a considerable drawback is the alkaline nature of the solutions obtained, which prevents extraction of acidic nitriles into organic solvents.